(a) Field of the Invention
The present invention relates to a humidity sensor and a fabricating method thereof, and more particularly, to a humidity sensor adopting an anodic aluminum oxide layer as a humidity sensing layer, and a fabricating method thereof.
(b) Description of the Related Art
Humidity sensors have been used in various fields, i.e., for cultivation of vegetables in greenhouses, home appliances such as a humidifier, a dryer, and an automatic cooker, humidity control in vehicles or buildings, etc.
In particular, a system-on-a-chip (SOC) realizing a system having various functions on one chip has been actively researched due to nanotechnology development in recent years. An operation frequency is continuously being increased and a minimum line width is continuously being decreased for effective information processing in a highly integrated chip or system. As long as this tendency is continued, parasitic effects, signal delay, and heat related problems are necessarily increased. Among the sub-effects, parasitic capacitances are causes for major losses of a high-frequency system, and are dependent primarily on humidity. Accordingly, sensing the humidity is required to predict and control performance of the high-frequency system.
The humidity sensors are classified as a capacitance type using a polymer, a conductivity type using a ceramic, and a type using an elastic surface wave element in accordance with an operational principle.
The conductivity type or the capacitance type mainly uses a polyimide, etc. as a humidity sensing material, and can measure humidity by using an inter-electrode resistance change or a capacitance change caused by absorption of moisture to the inside of a polymer through proper arrangement of electrodes at both ends or upper and lower sides of the polyimide.
When the moisture is absorbed in a polymer humidity sensing layer, inter-electrode resistance component is varied. At this time, the conductivity type of humidity sensor can measure a change in humidity by detecting the variation of the inter-electrode resistance component.
However, since the polymer humidity sensing layer uses a polymer as the humidity sensing material, the temperature is limited. When the temperature increases to 60° C. or more, the polymer which is an organic material is deformed. The humidity sensing function may be deteriorated by the deformation.
Further, when the polymer is exposed to an environment in which oil or other contaminants are generated for a long time, the surface of the humidity sensing layer is deteriorated or the moisture cannot infiltrate due to clogging of the surface, such that humidity sensing characteristics are deteriorated.
Meanwhile, the capacitance type of humidity sensor detects the change in humidity by measuring the magnitude of a capacitance variation depending on the amount of moisture inputted into the polymer humidity sensing layer. The capacitance type of humidity sensor may provide high precision in comparison with the conductivity type of humidity sensor due to an output characteristic having linearity, but since the capacitance type of humidity sensor uses the polymer, sensitivity and accuracy are deteriorated depending on temperature.
Further, the sensitivity and accuracy of the humidity sensing layer are increased as a surface area becomes larger. However, a process of forming a pattern having a structure of several tens of nanometers in a polymer layer is complicated and the manufacturing cost is increased.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.